// 通用防抖代码
export function debounce(func, delay) {
  let timer = null
  return function(...args) {
    clearTimeout(timer)
    timer = setTimeout(() => {
      func.apply(this, args)
    }, delay)
  }
}

/**
 * 检测图片是否存在, 自定义vue指令用
 * @param url
 */
function imageIsExist(url) {
  return new Promise((resolve) => {
    var img = new Image()
    img.onload = function() {
      if (this.complete == true) {
        resolve(true)
        img = null
      }
    }
    img.onerror = function() {
      resolve(false)
      img = null
    }
    img.src = url
  })
}

//全局注册自定义指令，用于判断当前图片是否能够加载成功，可以加载成功则赋值为img的src属性，否则使用默认图片
export async function realImg(el, binding) {
  //指令名称为：real-img
  let imgURL = binding.value //获取图片地址
  if (imgURL) {
    let exist = await imageIsExist(imgURL)
    if (exist) {
      el.setAttribute('src', imgURL)
    }
  }
}
